2. Three-Schema Architecture
Mappings among schema levels are needed
to transform requests and data.
Programs refer to an external schema,
and are mapped by the DBMS to the
internal schema for execution.
Data extracted from the internal DBMS
level is reformatted to match the user’s
external view (e.g. formatting the results
of an SQL query for display in a Web
There are two levels of mapping in the architecture
Conceptual/internal mapping defines the
correspondence between the conceptual view and
the stored database
An external/conceptual mapping defines the
correspondence between a particular external view
and the conceptual view
5. DBMS Languages
Data Definition Language (DDL)
Data Manipulation Language (DML)
Data Control Language (DCL)
High-Level or Non-procedural
Languages: These include the relational
6. DBMS Languages (cont’d)
Data Definition Language (DDL):
Used by the DBA and database designers to specify the conceptual
schema of a database.
In many DBMSs, the DDL is also used to define internal and
external schemas (views).
Data Manipulation Language (DML):
Used by the DBA for manipulation of records
Insertion,Updation ,Deletion and retrieval of record.
7. Data Control Language (DCL)
A Data Control Language (DCL):
DCL is a subset of SQL, used to control access to data
in a database.
Examples of DCL commands include:
GRANT to allow specified users to perform specified tasks.
REVOKE to cancel previously granted or denied permissions.
8. Host Language
A domain-specific language (DSL)
DSL is an Application Programming Interface
(either a Programming Language or executable
Specification Language?) whose grammar matches
the Problem Domain.
The biggest, most common example here is Structured
Query Language. It provides a declarative syntax, and
you call it from an Object Oriented application that uses
a procedural syntax.
9. Role of Database Administrator
Defining the conceptual schema
Defining the internal schema
Liaising with users
Defining security and integrity rules
Defining backup and recovery procedures
10. Basic 2-tier Client-Server
Specialized Servers with Specialized
Clients can access the specialized servers
as needed by the applications
11. Client/Server applications
Applications can be divided into categories:
First, user-written applications. (regular
application programs, written language
such as C or Java.
Second, vendor-provided applications
(often called tools). The overall purpose
of such tools is to assist in the process to
creating and executing other applications.
13. Two Tier Client-Server
A client program may connect to several
DBMSs, sometimes called the data sources.
In general, data sources can be files or other
non-DBMS software that manages data.
Other variations of clients are possible: e.g.,
in some DBMSs, more functionality is
transferred to clients including data
dictionary functions, optimization and
recovery across multiple servers, etc.
Provide appropriate interfaces through a
client software module to access and utilize
the various server resources.
Clients may be diskless machines or PCs or
Workstations with disks with only the client
Connected to the servers via some form of a
(LAN: local area network, wireless
15. DBMS Server
Provides database query and transaction services
to the clients
Relational DBMS servers are often called SQL
servers, query servers, or transaction servers
Applications running on clients utilize an
Application Program Interface (API) to access
server databases via standard interface such as:
ODBC: Open Database Connectivity standard
JDBC: for Java programming access
Client and server must install appropriate client
module and server module software for ODBC or
16. Client/Server Architecture
One client one Server (1:1)
Clients and Server running on different
20. Centralized DBMS Architectures
Combines everything into single system
including- DBMS software, hardware,
application programs, and user interface
User can still connect through a remote
terminal – however, all processing is
done at centralized site.
21. Distributed Processing
Distinct machines can be connected
together into a communications network
The term "parallel processing" is also
sometimes used with essentially the same
22. Distributed Architecture
Many Server many Clients (M:M)
Used at enterprise level
Each machine runs both clients and server
Data is spread across many machines
Application sometime needs the ability to access data from
more than one machines
Such access in two different ways:
A client be able to access any number of server but only one at a
The client might be able to access many servers simultaneously.
24. Three Tier Client-Server
Common for Web applications
Intermediate Layer called Application Server or Web
Stores the web connectivity software and the business logic
part of the application used to access the corresponding data
from the database server
Three-tier Architecture Can Enhance Security:
Database server only accessible via middle tier
Clients cannot directly access database server